Chip resistant primer composition V&#39;

ABSTRACT

Solvent-based thermosetting coating composition comprising a hydroxy functional epoxy ester resin, linear polycaprolactone diol, and blocked polyisocyanate crosslinking agent. The coating composition may be formulated as hot sprayable, high solids coating composition suitable for use as chip resistant automotive vehicle primer adapted for use on body panel areas subject to chipping by stones, gravel and other road debris. Alternatively, the composition may be formulated as a high solids composition sprayable with conventional spraying equipment. The hydroxy functional epoxy ester resin is formed by reaction of diepoxide chain extended with dicarboxylic acid and chain terminated with acid component comprising primary hydroxy functional acid.

Reference is made to concurrently filed and commonly assigned relatedU.S. application Ser. No. 800,887 entilted "Chip Resistant Primers V"and Ser. No. 800,942 entitled "Chip Resistsant Primers V"", both toKordomenos et al.

TECHNICAL FIELD

This invention relates to a solvent-based, thermosetting coatingcomposition comprising a hydroxy functional epoxy ester resin, a highmolecular weight linear polycaprolactone diol and blocked polyisocyanatecrosslinking agent. It relates also to such coating compositionformulated, for example, as a hot sprayable, high solids coatingcomposition suitable for use as a chip resistant automotive vehicleprimer adapted for use on body panel areas subject to chipping bystones, gravel and other road debris.

BACKGROUND

Automobile manufacturers, in their efforts to extend the expected lifeof automobile sheet metal and the like, have directed considerableattention to various processes and compositions designed to result innot only improved corrosion resistance but also improved chip resistanceproperties. In particular, research and development efforts haverecently been directed to obtaining primer compositions which areflexible and chip resistant and which give corrosion protection whileexhibiting good humidity and solvent resistance, as well as goodintercoat adhesion. New automobile designs and concern about chipping inareas exposed to stones, gravel and other road debris, e.g. rockerpanels, have demanded such chip resistant primers which can be appliedin reasonable thicknesses by techniques which do not require extensiveand expensive processing modifications during painting operations. Todate available primers, whether high or low solids, have not provensuitable.

In order to overcome the aforementioned chipping problem it has beencommon to apply relatively thick chip resistant coatings in body panelregions, which are inclined to chip, prior to application of stillanother primer composition. One such chip resistant sealer materialwhich has been employed is a polyvinyl chloride plastisol sealer whichhas been applied with airless spray gun equipment in thicknesses ofabout 20 mils in regions subject to high levels of chipping. Problemsattendant with such thick coatings are readily apparent. Because of thethickness in the region to which it is applied, these materials presentan appearance problem often resulting in waviness and roughness in thefinal coating on the sheet metal. Often times surface imperfections alsoresult from the fact that a primer is applied over the top of thissealer with the primer and sealer being cured together. As a result somesolvent and plasticizer tend to be driven out of the polyvinyl chlorideplastisol and result in a wavy and rough surface. Still further problemsassociated with the use of such polyvinyl chloride plastisol sealers andthe like involve application technique. Since the polyvinyl chlorideplastisol sealers and the like must be applied in thicknesses of 20 milsor greater in order to obtain good adhesion, they cannot be feathereddown to blend in with other regions of the sheet metal which do notrequire the additional chip protection. Thus, the materials must beapplied using a masking technique whereby those regions which are not tobe coated with the sealer material are masked in a separate operationprior to application of sealer. This masking is then removed after thesealer is applied. It would obviously be desirable to eliminate theseadditional steps in the application of the chip resistant sealermaterial.

Accordingly, it is a preferred object of this invention to provide anovel solvent based, thermosetting coating composition adapted for useas a chip resistant primer, which primer may be applied in thicknessesof less than 20 mils and which may be feathered in such a manner as toblend with paint in other areas of the substrate to be painted which donot require chip resistant coating.

It is another object of the invention to provide novel coatingcompositions which comprise crosslinkable hydroxy functional epoxy esterresins, a high molecular weight linear polycaprolactone diol and blockedpolyisocyanate crosslinking agent, which provide high crosslinkingefficiency and tough, well cured films at minimum bake temperatures suchas when applied as automotive primers. In this regard, it is aparticular object of the invention to provide thermosetting coatingcomposition of sufficiently low Volatile Organic Content (VOC) to aid inmeeting governmental emission guidelines and yet which can be applied toa substrate by spraying or other known method.

It is another object of the invention to provide a composition whichwill form a coating on a substrate, which coating has advantageousphysical properties including, for example, humidity and solventresistance, flexibility and corrosion protection for the underlyingsubstrate.

Additional aspects and advantages of the invention will be apparent fromthe following description thereof.

DISCLOSURE OF THE INVENTION

According to the present invention, novel thermosetting coatingcompositions are provided which are especially advantageous for use ashigh solids organic solvent based thermosetting compositions to providechip resistant coatings. A coating composition of the invention, inaddition to solvent and any pigments and additives such as, for example,catalysts, flow control agents and the like, comprises:

(A) hydroxy functional epoxy ester resin having a number avergemolecular weight (Mn) between about 1,000 and about 4,000 and being thereaction product of diepoxide chain extended with dicarboxylic acid andeither subsequently or simultaneously chain terminated with acidcomponent comprising primary hydroxy functional acid;

(B) linear polycaprolactone diol having a molecular weight of betweenabout 1500 and about 500, wherein (A) and (B) are included in thecomposition in a weight ratio between about 4:1 and 1:4; and

(C) blocked polyisocyanate crosslinking agent comprising at least twoisocyanate groups which have been blocked by reaction with an activehydrogen bearing blocking agent which de-blocks at the cure temperatureof the composition, the crosslinking agent being included in thecomposition in an amount equal to between about 10 and about 50 percentof the combined weight of (A) and (B) in the composition.

Particularly preferred compositions of the invention are thoseformulated as high solids coating compositions having solids levels inthe range of 65-80% solids and which are applied as chip resistantprimers in those areas of automotive panels, such as rocker panels,which are exposed to high levels of chipping. Such compositions may beapplied in thicknesses ranging from 1 to 25 mils wet to obtain finalcoatings in the range of 1 to 12 mils dry, and may be feathered down toblend in with paint applied to regions outside that requiring additionalchip resistance protection. Generally, the compositions of this solidslevel may be applied using hot spray equipment at temperatures in therange of room temperature, i.e. about 70° F., to about 160° F.

Other preferred compositions of the invention are those formulated ashigh solids coating compositions adapted to be applied by conventionalspraying onto a substrate. These high solids coating compositions mayhave a solids level in the range of 50-60% and are especially useful asa primer coating on the bare, unpolished metal surface of an automotivevehicle. As used herein, a high solids coating composition is one havinga volatile organic content of about 479 g/l (4.0 lb./gal.) or less.

Other features and advantages of this invention will become moreapparent from the following, detailed description thereof including thepreferred embodiments and best mode of carrying out this invention.

DETAILED DESCRIPTION OF THE INVENTION

Thermosetting coating compositions of the invention comprise hydroxyfunctional epoxy ester resin, high molecular weight linearpolycaprolactone diol and block polyisocyanate crosslinking agent. Thehydroxy functional epoxy ester resin has a number average molecularweight (Mn) of between about 1,000 and about 4,000 and is the reactionproduct of diepoxide chain extended with dicarboxylic acid and eithersubsequently or simultaneously chain terminated with acid componentcomprising primary hydroxy functional acid. The linear polycaprolatonediol has a molecular weight of between about 1500 and about 5000,preferably between about 2000 and about 4000. These polycaprolactonediols may be prepared by polymerizing lactone monomers, preferablyepsilon-caprolactone monomers, with initiators comprising one or morecompounds having two functional groups each having an active hydrogen.The epoxy ester resin and the polycaprolactone diol are included in thecomposition in a weight ratio of between about 1:4 and 4:1, preferablyin a weight ratio of about 1:1.

The blocked polyisocyanate crosslinking agent comprises at least twoisocyanate groups which have been blocked by reaction with an activehydrogen bearing blocking agent which deblocks at the cure temperatureof the composition. The blocked polyisocyanate crosslinking agent isincluded in the composition in an amount equal to between about 10 andabout 50 weight percent, preferably between about 20 and 40 weightpercent, the combined weight of hydroxy functional epoxy ester resin andlinear polycaprolactone diol in the coating composition. The blockedpolyisocyanate crosslinking agent preferably is selected from the groupconsisting of, but not necessarily limited to, blocked trifunctionalisocyanurate ring containing polyisocyanates and oligoester modifiedblocked isocyanates.

It is believed to be a significant characterizing aspect of the coatingcomposition of the present invention that the polycaprolactone diolportion of the composition gives the cured composition flexibility aswell as toughness, two key properties when choosing a primer for use inareas susceptible to chipping. It is a further characterizing aspect ofthe cured composition that it includes epoxy resin portions, i.e., fromthe hydroxy functional epoxy ester resin, which give the curedcomposition excellent corrosion resistance properties. Preferred hydroxyfunctional epoxy ester resins of the invention include significantaromatic content which is believed to enhance corrosion resistanceproperties. Even though aromatics tend to increase the brittleness ofpolymers and compositions including such polymers, it is possible toinclude them since, as mentioned above, the polycaprolactone portion ofthe cured composition gives the composition increased flexibility whichcan more than compensate for any such brittleness. A particularlypreferred embodiment of the hydroxy functional epoxy ester resin of theinvention is prepared from aromatic containing diepoxide. Also, asdiscussed hereafter, the dicarboxylic acid reactant employed inpreparation of the hydroxy functional epoxy ester resin may also includearomatic units.

Each of the above major components of the compositions as well as othercomponents and other aspects of the invention are described hereinafterin greater detail.

A. HYDROXY FUNCTIONAL EPOXY ESTER RESIN

As described above, this resin is the reaction product of diepoxidechain extended with dicarboxylic acid and either subsequently orsimultaneously chain terminated with hydroxy functional acid componentcomprising primary hydroxy functional acid.

Each of the reactants employed in the preparation of the hydroxyfunctional epoxy ester resin is described in greater detail below.

(i) Diepoxide Reactant

The diepoxide reactant employed in the manufacture of the hydroxyfunctional epoxy ester resin can be any of numerous diepoxides includingdiphenol chain extended epoxides, many of which are commerciallyavailable and which will be apparent to the skilled in the art in viewof the present disclosure. While, ultimately, the choice of the epoxidereactant for preparing the hydroxy functional epoxy ester resin willdepend to an extent upon the particular application intended for thecoating composition, terminal diepoxides, that is diepoxides bearing twoterminal epoxide groups, are generally most preferred. These aregenerally more reactive and therefore require reaction conditions underwhich undesirable side reactions, for example, epoxy-epoxy reactions andgellation, can be more easily avoided. The diepoxides which are to bechain extended with dicarboxylic acid may be selected from numerousdiepoxides, some of which may be diphenol extended diepoxides.

Diepoxy resins, not previously extended with diphenol, may be used inthe preparation of the hydroxy functional epoxy ester resin. Preferreddiepoxy resins of this type include Epon 828 (trademark) and Epon 829(trademark), which are non-extended diepoxides of the Epon Series, ShellChemical Company, Houston, Tex., as well as cycloaliphatic diepoxyresins, such as the Eponex (trademark) series, Shell Chemical Company;hydantoin epoxy resins such as, for example, Resin XB2793 (trademark)Ciba-Geigy Corporation, Ardsley, N.Y.; and any of a wide variety ofacyclic or cyclic aliphatic diepoxides such as, for example,1,4-butanediol diglycidyl ether and 4-vinyl-cyclohexene dioxide and thelike. Still other suitable diepoxides which may be chain extended withdicarboxylic acid in synthesizing the epoxy ester resin are commerciallyavailable and will be apparent to the skilled of the art in view of thepresent disclosure.

Still further, diepoxides previously extended with diphenol may be usedin forming the hydroxy functional epoxy ester resin and numerous suchmaterials are commercially available. These include certain of the wellknown bisphenol-A epichlorohydrin epoxy resins of the aforementionedEpon (trademark) series, e.g. Epon 1000 and Epon 1004 and the DER(trademark) series, Dow Chemical Company, Midland, Mich., e.g., DER 332.These diglycidyl ether bisphenol-A resins or higher molecular weightanalogs thereof, are most preferred in view of their cost and commercialavailability. Also, it will be understood from the foregoing that anymixture of compatible diepoxides may be used.

In addition to the diepoxide, a portion of the epoxy functionality canbe provided by any compatible monoepoxy compound or polyepoxy compoundor mixture of such compounds. The polyepoxide can be any of the wellknown types such as polyglycidyl ethers of polyphenols. These can beproduced by etherification of polyphenol with epihalohydrin in thepresence of alkali. It will be recognized by the skilled of the art inview of the present disclosure, that in some instances, particularlywhere a coating composition of high solids content is less important, itmay be desirable to incorporate polyepoxide of higher molecular weight.Preferably, any such polepoxide contains free hydroxyl groups inaddition to epoxide groups.

While polyglycidyl ethers of polyphenol can be employed, it may bedesirable to react a portion of the reactive sites (hydroxyl or in someinstances epoxy) with a modifying material to vary the filmcharacteristics of the resin. The epoxy resin may be modified, forexample, with isocyanate group containing organic materials or otherreactive organic materials.

Other useful polyepoxides are the novolak resins including, for example,the novolak epoxy resins ECN 1235 (trademark) and ECN 1273 (trademark),Ciba-Geigy Corporation.

According to preferred embodiments of the present invention, epoxidecompounds other than diepoxide compounds provide no more than about 15%and most preferably substantially none of the total epoxidefunctionality in the reactants used to form the epoxy ester resin.

(ii) Dicarboxylic Acid Reactant

Dicarboxylic acids suitable for chain extending diepoxides discussedabove preferably have a number average molecular weight of between about145 and about 1000 and more preferably between about 400 and about 600.Suitable dicarboxylic acids includes numerous commercially availablematerials, many of which will be readily apparent to the skilled of theart in view of the present disclosure. Suitable dicarboxylic acidsinclude saturated or unsaturated, cyclic or acyclic, aliphatic oraromatic dicarboxylic acids or a mixture thereof. Acyclic aliphaticdicarboxylic acids are generally preferred in view of the enhancedflexibility they provide to the cured coatings of the invention.Preferred dicarboxylic acids have the general formula (I):

    HOOC--R--COOH                                              (I)

wherein R is a divalent linking moiety substantially unreactive with thediepoxide resin. It will be apparent to the skilled of the art in viewof the present disclosure, that R should be substantially unreactivealso with the acid component employed in preparation of the epoxy esterresin, and with hydroxy functionality (generated in the chain-extensionreaction). Preferably R is a divalent, organic, linking moiety.Particularly preferred are those dicarboxylic acids wherein R isselected, from the group comprising a straight or branched alkylene oralkylidene moiety, preferably of about 4-42 carbons, for example,(CH₂)_(n) wherein n is preferably from about 4 to about 42, and the likeor a mixture thereof. Dicarboxylic acids of this character have beenfound to provide good reactivity with the preferred diepoxides describedabove and to provide, ultimately, cured coatings of the invention havingexcellent physical properties, most notably excellent flexibility andcorrosion protection

Exemplary dicarboxylic acids include adipic acid,3,3-dimethylpentanedioic acid, benzenedicarboxylic acid,phenylenediethanoic acid, naphthalenedicarboxylic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, and the like or a compatiblemixture of any of them. The anhydrides of these acids, where theanhydrides exist, are, of course, embraced in the term "acid" since thereaction products obtained therefrom are the same. While dicarboxylicacids according to formula (I) can be used, wherein R is an alkylenechain of less than 4 carbons, for example, oxalic acid, malonic acid,succinic acid, glutaric acid and the like, these are less preferred inview of the somewhat lesser degree of flexibility provided thereby.Preferably the dicarboxylic acid provides two terminal carboxyl groups.Similarly, preferred aromatic dicarboxylic acids are those wherein thecarboxylic groups are more spaced apart, for example,1,4-benzenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid.

The most preferred dicarboxylic acids are substantially saturated,acyclic, aliphatic dimer acids, which are well known to the skilled ofthe art and readily commercially available. These are typically thedimerization reaction products of fatty acids which have from 4 to 22carbons and a terminal carboxyl group. Of these, dimer acid of 36carbons is most preferred since it provides excellent reactivity withthe preferred diepoxides described above, provides epoxy ester reactionproducts of advantageously wide molecular weight distribution, andprovides, ultimately, cured coatings of the invention having excellentphysical properties. In addition, dimer acid of 36 carbons is readilycommercially available, for example, as Empol 1014 (trademark), Empol1016 (trademark) and Empol 1018 (trademark, each available from EmeryIndustries, Inc., Cincinnati, Ohio. It should be recognized that most orall commercially available dimer acids contain some portion of trimeracid, typically, for example, about 5-10% but in some cases as much as30% or more, and also contain a usually smaller portion ofmonocarboxylic acid. As used herein, the term "dimer acid" includesthose containing such amounts of these materials. Most useful is thepresent compositions are products that contain mostly dibasic acid andnone or low amounts of tribasic and monobasic acids.

Aliphatic dicarboxylic acids are seen to provide additional advantages.In particular, while not wishing to be bound by theory, it is presentlyunderstood that hydroxy functional epoxy ester resin derived therefromwet the substrate surface better and provide enhanced adhesion betweenthe substrate and the cured coating. They also flow better and, thus,provide an excellent smooth surface upon being cured. Also, thealiphatic units provide enhanced flexibility to the cured coating, asnoted above, and this flexibility of the coating is seen to provideenhanced impact resistance, a feature even more highly desirable forchip resistant coating embodiments.

Where corrosion protection for the substrate is important, it may bepreferred to employ dicarboxylic acid according to formula (I) above,wherein R is, at least in part, aromatic. As noted above, it is believedthat such aromatics in the coating composition of the invention, such asa primer composition for a metal substrate, are more resistant tohydrolysis than are aliphatics and, therefore, provide enhancedcorrosion and moisture resistance. Of course, as also noted above,according to preferred embodiments of the epoxy ester resin precursor,described above, the diepoxide reactant provides aromatic units to theresin and this would similarly contribute to corrosion and moistureresistance.

Other suitable dicarboxylic acids for forming the hydroxy functionalepoxy ester resin of the present invention will be apparent to theskilled of the art in view of the present disclosure.

Preferably, the chain extended diepoxide to be terminated with acidcomponent has a number average molecular weight (Mn) between about 1,200and about 3,500, and more preferably between about 1,600 and about2,400.

(iii) Acid Component Reactant

The acid component comprises primary hydroxy functional acid. Numeroussuitable primary hydroxy functional acids will be apparent to theskilled of the art in view of the present disclosure, including manywhich are readily commercially available. These include C₃ -C₂₆ primaryhydroxy functional acids, wherein the acid contains one carboxyl groupand one or more hydroxyl groups (at least one of which is a primaryhydroxyl group) and no other functional groups which would substantiallyinterfere with the preparation of the hydroxyl functional epoxy esterresin, i.e., wherein any other functional groups would be substantiallyunreactive with the chain-extension reactants or reaction product.Preferred primary hydroxy functional acids correspond to the generalchemical formula: ##STR1## wherein R₁, R₂, R₃ and R₄ are the same ordifferent and each preferably is lower alkylene such as methylene orethylene, and Z and Z' are selected independently from hydrogen,hydroxyl, and any other non-interfering functionality such as nitrileester group, halogen, amide, etc. Suitable hydroxy acids which may beemployed in the chain terminating reaction include, but are not limitedto, dimethylolpropionic acid which is most preferred,bis(hydroxyethyl)propionic acid, bis(hydroxypropyl)propionic acid, andthe like and a compatible mixture of any of them. Preferably, theprimary hydroxy acid contains two or more hydroxyl groups, e.g., atleast one of Z and Z' contains a hydroxyl group.

Optionally, the acid component may further comprise fatty acid. Suitablefatty acids include numerous commercially available fatty acids such as,for example, those derived from or contained in either animal orvegetable fat or oil. Preferred are fatty acids from about 8 to about 18carbons, since these are found to provide flexibility to the curedcoating. Also preferred among the fatty acids are the more saturatedfatty acids, since it appears that olefinic unsaturation in the fattyacid can undergo a polymerization-type reaction between such doublebonds during the synthesis of the epoxy ester resin of the invention.Unsaturated fatty acids are suitable for use, however, such as, forexample, oleic acid, linoleic, linolenic and the like and mixtures ofsuch acids, and can be used together with a suitable inhibitor for thepolymerization-type reaction such as hydroquinone or the like, of whichmany are commercially available and will be apparent to the skilled ofthe art in view of the present disclosure. In addition, aromatic fattyacids are commercially available and can be employed. Preferred for useare the substantially saturated fatty acids such as Soya fatty acidwhich is most preferred, and butyric, lauric, palmitic and stearic fattyacids and the like or a compatible mixture of any of them. These arerelatively inexpensive and have been found to provide good reactivitywith the preferred diepoxides described above. For convenience of use,the fatty acids which are semisolid or liquid at room temperature aregenerally preferred over the solid fatty acids.

The hydroxy functional epoxy ester resin of the invention can be madeaccording to techniques well known to the skilled of the art. The chainextension, where necessary, and chain termination reactions may becarried out sequentially, with the chain extension of the diepoxidebeing carried out first. According to the sequential technique,diepoxide and dicarboxylic acid are charged into a suitable reactor andheated. It should be recognized that to assure rapid and/or morecomplete reaction of the diepoxide with the dicarboxylic acidfunctionality, it is usually preferred to have a catalyst present. Thereactants are used in relative proportions to yield a chain extensionreaction product bearing two unreacted epoxy groups and preferablysubstantially no unreacted carboxyl functionality. Suitable separationtechniques are known to the skilled of the art for removal of unusedreactants. The use of catalyst has been found to provide advantageousepoxy ester resin of the invention and is preferred. Epon 829(trademark), mentioned above, as sold, provides a proprietary catalyst.Epon 828 (trademark), is substantially the same but does not providesuch catalyst. Suitable catalysts are commerically available and includeany of the well known catalysts for epoxy-dicarboxylic acid reactionssuch as, for example, sodium carbonate which is preferred, and lithiumneodecanoate, lithium naphthenate, lithium nanoate, other knownorganometallic catalysts and tertiary amine catalysts and the like or acompatible mixture of any of them. Still other preferred catalystsinclude formylmethylene triphenylphosphorane, formylmethyltriphenylphosphonium chloride, methyltriphenylphosphonium iodide,ethyltriphenylphosphonium acetate. Others will be apparent to theskilled of the art in view of the present disclosure.

The reaction mixture is heated to at least about 140° C. (250° F.). Whenin the presence of catalyst, exothermic reaction will proceed with orwithout further heating. Typically, the reaction mixture will then reachabout 149° C.-176° C. (300° F.-350° F.), depending upon the batch sizeand reactor vessel insulation, ect. In the absence of catalyst, suchexotherm is typically not observed and continued heating is required.The progress of the reaction can be followed by measuring the acidnumber and/or weight per epoxide (WPE).

The diepoxide and dicarboxylic acid are generally reacted in relativeproportions of from about 1:0.5 to about 0.8 equivalents, respectively.Preferred relative proportions are one equivalent of epoxy functionalityto 0.5 to 0.6 equivalents of dicarboxylic acid functionality.

After completion of the above chain extension reaction of diepoxide withthe dicarboxylic acid, the acid component is charged into the reactionvessel. The reaction is exothermic and drives itself to completion. Thechain extended reaction product is reacted with the acid component inchain terminating reaction in preferably approximately 1 to 1 equivalentratio. This ratio is preferred since excess epoxy could result ingelation of the reaction mixture.

Alternatively the hydroxy functional epoxy ester resin may be made by asimultaneous technique, whereby the reactants are combined and reactedin a single batch. Due to the relative reactivity of the functionalgroups, the chain extension and the chain termination reactions willboth take place. If the reactions are carried out simultaneously, thereactants are used in amounts suitable to yield the desired reactionratio in view of the relative reactivity of the dicarboxylic acid andthe acid component, and in view of the desired molecular weight for thereaction product. It appears that present invention compositionscomprising hydroxy functional epoxy ester resin made by the simultaneousreaction technique have lower viscosities and, thus, are more easilysprayable than similar compositions having the same solids level andcomprising such hydroxy functional epoxy ester resins made by thesequential reaction technique.

(B) LINEAR POLYCAPROLACTONE DIOL

The linear polycaprolactone diol employed in the coating composition ofthe present invention has a molecular weight of between about 1500 andabout 5000, preferably between about 2000 and about 4000. Suitable suchpolycaprolactone diols can be formed by polymerizing lactones in thepresence of an initiator by methods well known to those skilled in theart. Such linear polycaprolactone diols also are commercially available,for example, from Union Carbide, Danbury, Conn. in the TONE (trademark)series, e.g., TONE 0260. This series comprises polycaprolactone diols aswell as polycaprolactone triols.

The preparation of suitable linear polycaprolactone diols is described,for example, in U.S. Pat. Nos. 2,914,556 and 3,169,945 to Hostettler etal. Polymerization of the lactone monomer to form the polycaprolatonediol of this invention is initiated by reaction with one or morecompounds having two functional groups each having an active hydrogencapable, with or without the aid of a catalyst, of opening the lactonering and adding it as an open chain without forming water ofcondensation. Compounds suitable for use to initiate the polymerizationof the lactones, referred to herein as initiators, include but are notlimited to, diamines, diols, amino alcohols, diacids, andhydroxy-carboxylic acids. Also suitable are amides, sulfonamides,hydrozones, carbazone, and oximes containing two reactive groups. Thelactone starting material which may be employed in forming thepolycaprolactone diol component of the invention may be any lactone, orcombination of lactones, having at least six carbon atoms, for example,from six to eight carbon atoms, in the ring and at least one hydrogennsubstituent on the carbon atom which is attached to the oxy group insaid ring. In one aspect, the lactone used as a starting material can berepresented by the general formula: ##STR2## in which n is at leastfour, for example, from four to six, at least n+2R's are hydrogen, andthe remaining R's are substituents selected from the group consisting ofhydrogen, alkyl, cycloalkyl, alkoxy and single ring aromatic hydrocarbonradicals. Lactones having greater numbers of substituents other thanhydrogen on the ring, and lactones having five or less carbon atoms inthe ring, are considered unsuitable for the purposes of the inventionbecause of the tendency that polymers thereof have to revert to themonomer, particularly at elevated temperature.

The lactones preferred in this invention for forming thepolycaprolactone diol are the epsilon-caprolactones having the generalformula: ##STR3## wherein at least six of the R's are hydrogen and theremainder are hydrogen, alkyl, cycloalkyl, alkoxy or single ringaromatic hydrocarbon radicals, none of the substituents contain morethan about twelve carbon atoms, and the total number of carbon atoms inthe substituents on a lactone ring does not exceed about twelve.Unsubstituted epsilon-caprolactone, in which all the R's are hydrogen,is derived from 6-hydroxyhexanoic acid and is most preferred.Substituted epsilon-caprolactones, and mixtures thereof, are availableby reacting a corresponding substituted cyclohexanone with an oxidizingagent such as peracetic acid.

Among the substituted epsilon-caprolactones considered most suitable forthe purposes of the invention are the various monoalkylepsilon-caprolactones such as the monomethyl-, monoethyl-, monopropyl-,monoisopropyl-, etc. to monododecyl epsilon-caprolactones; dialkylepsilon-caprolactones in which the two alkyl groups are substituted onthe same or different carbon atoms, but not both on the epsilon carbonatom; trialkyl epsilon-caprolactones in which two or three carbon atomsin the lactone ring are substituted, so long as the epsilon carbon atomis not disubstituted; alkoxy epsilon-caprolactones such as methoxy andethoxy epsilon-caprolactones; and cycloalkyl, aryl, and aralkylepsilon-caprolactones such as cyclohexyl, phenyl and benzylepsilon-caprolactones.

Lactones having more than six carbon atoms in the ring, e.g.,zeta-enatholactone and eta-caprylolactone may also be polymerized toform the linear polycaprolactone diol employed in the invention.

Diols that are suitable as bifunctional initiators include glycols ofthe formula HO(CH₂)_(n) OH in which n equals 2 to 10, glycols of theformula HO(CH₂ CH₂ O)_(n) H and HO(CHCH₃ CH₂ O)_(n) H in which n equals1 to 40, such as ethylene glycol, diethylene glycol, and the like,2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol,3-methyl-1,5-pentanediol, N-methyl- and N-ethyl-diethanol amines,various cyclohexanediols such as 4,4'-methylenebiscyclohexanol,4,4'-isopropylidenebiscyclohexanol, various xylenediols, varioushydroxymethyl-phenethyl alcohols, various hydroxymethyl-phenylpropanols,various phenylenediethanols, various phenyldipropanols, and variousheterocyclic diols such as 1,4-piperazinediethanol. Other suitable diolsinclude polyoxyalkylated derivatives of difunctional compounds havingtwo reactive hydrogen atoms. These difunctional compounds may containprimary or secondary hydroxyls, phenolic hydroxyls, primary or secondaryamino groups, amido, hydrazino, guanido, ureido, mercapto, sulfino,sulfonamide, or carboxyl groups. They are obtainable by reacting diolsof the class HO(CH₂)_(n) OH, wherein n equals 2 to 10, propylene glycol,thiodiethanol, xylenediols, 4,4'-methylenediphenol,4,4'-isopropylidenediphenol, and resorcinol; mercapto alcohols, likemercaptoethanol; dibasic acids, such as maleic, succinic, glutaric,adipic, pimelic, sebacic, phthalic, tetrahydrophthalic, andhexahydrophthalic; phosphorous acid; aliphatic, aromatic andcycloaliphatic primary monoamines, like methylamine, ethylamine,propylamine, butylamine, aniline, cyclohexylamine; secondary diamines,like N,N'-dimethylethylenediamine; and amino alcohols containing asecondary amino group, like N-methylethanolamine, with alkylene oxidessuch as ethylene oxide, propylene oxide, 1-butylene oxide, 2-butyleneoxide, isobutylene oxide, butadiene monooxide, styrene oxide, and alsomixtures of these monoepoxides.

Other useful bifunctional initiators are polymers of monoepoxidesobtainable by polymerizing with such catalyst as oxonium salts ofhydrogen halides; metal or nonmetal halides whose etherates are oxoniumcomplexes; electrophilic metal or non-metal halides in the presence ofhydrogen halides, acyl halides, or anhydrides of inorganic and organicacids; and inorganic acids or anhydrides thereof whose anions showlittle tendency to polarize. Polymers containing hydroxyl end groups canbe obtained by treating these products with alkaline reagents uponcompletion of the polymerization reaction. Among suitable monoepoxidesfor preparing such polymers are tetrahydrofuran, trimethylene oxide,propylene oxide, ethylene oxide and mixtures thereof.

Difunctional amino alcohols capable of initiating the polymerization oflactones include aliphatic amino alcohols of the general formulaHO(CH₂)_(n) NH₂, wherein n equals 2 to 10, N-methylethanolamine,isopropanolamine N-methylisopropanolamine, aromatic amino alcohols likepara-amino-phenethyl alcohol, and para-amino-alphamethylbenzyl alcohol,and various cycloaliphatic amino alcohols like 4-amino-cyclohexanol.

Suitable diamines include aliphatic diamines of the general formula H₂N(CH₂)_(n) NH₂, monosecondary diamines of the general formulaR"NH(CH₂)_(n) NH₂, and disecondary diamines of the general formulaR"NH(CH₂)_(n) NHR", where n equals 2 to 10 and where R" is alkyl, aryl,aralkyl or cycloalkyl; aromatic diamines, like metaphenylenediamine,para-phenylenediamine, toluene-2,4-diamine, toluene-2,6-diamine,1,5-naphthalenediamine, 1,8-naphthalenediamine, meta-xylylenediamine,para-xylylenediamine, benzidine, 3,3'-dimethyl-4,4'-biphenyldiamine,3,3'-dimethoxy-4,4'-biphenyldiamine, 3,3'-dichloro-4,4'-biphenyldiamine,4,4'-methylenedianiline, 4,4'-ethylenedianiline,2,3,5,6-tetramethyl-para-phenylenediamine, 2,5-fluorenediamine, and2,7-fluorenediamine; and cycloaliphatic diamines like1,4-cyclohexanediamine, 4,4'-methylenebiscyclohexylamine, and4,4'-isopropylidenebiscyclohexylamine; and heterocyclic amines such aspiperazine, 2,5-dimethylpiperazine, and1,4-bis(3-aminopropyl)piperazine.

Representatives of the many dicarboxylic acids that are suitable asbifunctional initiators are such dicarboxylic acids as oxalic acid,succinic acid, maleic acid, glutaric acid, adipic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, 4,4'-oxydibutyric acid,5,5'-oxydivaleric acid, 6,6'-oxydihexanoic acid, 4,4'-thiodibutyricacid, 5,5'-thiodivaleric acid, 6,6'-thiodihexanoic acid, itaconic acid,phthalic acid, isophthalic acid, terephthalic acid, 1,5-naphthoic acid,2,7-naphthoic acid, 2,6-naphthoic acid, 3,3'-methylenedibenzoic acid,various tetrahydrophthalic acids, and various hexahydrophthalic acids.Suitable hydroxy- and aminocarboxylic acids include 2-hydroxypropionicacid, 6-hydroxycaproic acid, 11-hydroxy-undecanoic acid, salicylic acid,parahydroxybenzoic acid, beta-alanine, 6-aminocaproic acid,7-aminoheptanoic acid, 11-amino-undecanoic acid, and paraaminobenzoicacid.

The initiator is believed to open the lactone ring to produce an esterof amide having two terminal groups that are capable of opening furtherlactone rings and thereby of adding more and more lactone to themolecule. Thus, for example, the polymerization of epsilon-caprolactoneinitiated with a diol is believed to take place primarily as follows:##STR4## wherein a is the total number of mols of lactone reacted permol of initiator and b+c=a.

To initiate and continue the polymerization of the lactone, the lactoneand the initiator are preferably heated to a temperature between about130° and 200° C. in order to achieve a practical and desirable rate ofreaction with a minimum of decomposition. The temperature may beconsiderably lower however, i.e., as low as about 50° C. at thesacrifice of speed of reaction. It may also be considerably higher,i.e., up to about 300° C., although care must be taken at such highertemperatures because of the more likely losses, at temperatures above250° C., due to decomposition or undesirable side reactions. Generally,therefore, a temperature range of 50° to 300° C. is considered operableand a more limited range between about 130° and 200° C. is consideredpreferable.

It is within the ability of those skilled in the art to determine asuitable amount of initiator to use to achieve a linear polycaprolactonediol product of desired molecular weight. The polymerization may be, andpreferably is, carried out with the use of a catalyst, such as a basicor neutral ester interchange catalyst, to accelerate the reaction. Amongcatalysts suitable for this purpose are such metals as lithium, sodium,potassium, rubidium, cesium, magnesium, calcium, barium, strontium,zinc, aluminum, titanium, cobalt, germanium, tin, lead, antimony,arsenic and cerium, as well as the alkoxides thereof. Additionalsuitable catalysts are, by way of example, the carbonates of alkali- andalkaline earth metals, zinc borate, lead borate, zinc oxide, leadsilicate, lead arsenate, litharge, lead carbonate, antimony trioxide,germanium dioxide, cerium trioxide, cobaltous acetate and aluminumisopropoxide. Catalyst concentrations between about 0.001 and 0.5%,based on the weight of the starting lactones, are suitable. Thepreferred range is from 0.01 to 0.2%.

While not wishing to be board by theory, it is presently believed thatthe linear polycaprolactone diol is characterized by the presence ofseries of interconnected, substantially linear units or groups composedof carbon, hydrogen and oxygen. The interconnected units are openedlactone residues each having a terminal oxy group at one end, a carbonylgroup at the other end, an intermediate chain of at least five carbonatoms and at least one hydrogen substituent on the carbon atom in theintermediate chain that is attached to the terminal oxy group. The oxygroup of one lactone residue is connected to the carbonyl group of anadjacent lactone residue in the series and the oxy group of the lastlactone residue in a series is connected to a hydrogen to form aterminal hydroxyl group at the end of the series.

The hydroxy functional epoxy ester resin and the linear polycaprolactonediol are included in the coating composition in a weight ratio ofbetween about 1:4 and 4:1, preferably in a weight ratio of about 1:1.

C. BLOCKED POLYISOCYANATE CROSSLINKING AGENT

The crosslinking agent employed in the novel solvent based coatingcompositions of the invention comprises blocked polyisocyanate. Thenovel solvent based coating compositions of the invention, as a resultof employing blocked polyisocyanate crosslinking agents, exhibitexceptional shelf stability even when corrosion inhibiting pigments suchas zinc chromate are used in high concentrations.

As used herein "blocked polyisocyanate" means an isocyanate compoundcontaining two or more isocyanate groups, all of which have been reactedwith a material which will prevent reaction of the isocyanate group atroom temperature with compounds that conventionally react with suchgroups, and at least some of which will permit that reaction to occur athigher (cure) temperatures. In general the blocked polyisocyanate may beprepared by reacting a sufficient quantity of an active hydrogencontaining blocking agent with the polyisocyanate to insure that no freeisocyanate groups are present. The blocking agent may be represented bythe formula BH and may be selected from numerous materials, hereinafterdiscussed, which bear an active hydrogen.

The blocked polyisocyanate crosslinking agent is included incompositions of the invention in an amount equal to between about 10 andabout 50 percent, preferably in an amount equal to between about 20 andabout 40 percent, of the combined weight of hydroxy functional epoxyester resin (A) and linear polycaprolactone diol (B) in the coatingcomposition. Blocked polyisocyanates of numerous types may be employedin the compositions of the invention.

Particularly suitable blocked polyisocyanates, which will be discussedfurther hereinafter, include blocked polymethylene polyphenolisocyanates, isocyanurate ring containing blocked polyisocyanates andcertain oligoester modified blocked polyisocyanates.

In the preparation of the blocked polyisocyanate crosslinking agent, anysuitable organic polyisocyanate may be used. Representative examples arethe aliphatic compounds such as trimethylene, tetramethylene,pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene,2,3-butylene, 1,3-butylene, ethylidene and butylidene diisocyanates; thecycloalkylene compounds such as 1,3-cyclopentane, 1,4-cyclohexane, and1,2-cyclohexane diisocyanates; the aromatic compounds such asm-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene, and1,4-naphthalene diisocyanates, the aliphatic-aromatic compounds such as4,4'-diphenylene methane, 2,4- or 2,6-tolylene, or mixtures thereof,4,4'-toluidine, and 1,4-xylylene diisocyanates; substituted aromaticcompounds such as dianisidine diisocyanate, 4,4'-diphenyletherdiisocyanate and chlorodiphenylene diisocyanate; the triisocyanates suchas triphenyl methane-4,4'4"-triisocyanate, 1,3,5-triisocyanate benzeneand 2,4,6-triisocyanate toluene; the tetraisocyanates such as4,4'-diphenyl-dimethyl methane-2,2',5,5'-tetraisocyanate; and thepolymerized polyisocyanates such as tolylene diisocyanate dimers andtrimers, and the like.

In addition, the organic polyisocyanate may be a prepolymer derived froma polyol including polyether polyol or polyester polyol, includingpolyethers which are reacted with excess polyisocyanates to formisocyanate-terminated prepolymers. The polyols may be simple polyolssuch as glycols, e.g., ethylene glycol and propylene glycol, as well asother polyols such as glycerol; trimethylolpropane, pentaerythritol, andthe like, as well as mono-ethers such as diethylene glycol, tripropyleneglycol and the like and polyethers, i.e., alkylene oxide condensates ofthe above. Among the alkylene oxides that may be condensed with thesepolyols to form polyethers are ethylene oxide, propylene oxide, butyleneoxide, styrene oxide and the like. These are generally calledhydroxyl-terminated polyethers and can be linear or branched. Examplesof polyethers include polyoxyethylene glycol, polyoxypropylene glycol,polyoxytetramethylene glycol, polyoxyhexamethylene glycol,polyoxynonamethylene glycol, polyoxydecamethylene glycol,polyoxydodecamethylene glycol and mixtures thereof. Other types ofpolyoxyalkylene glycol ethers can be used. Especially useful polyetherpolyols are those derived from reacting polyols such as ethylene glycol,diethylene glycol, triethylene glycol, 1,4-butylene glycol, 1,3-butyleneglycol, 1,6-hexanediol, and their mixtures; glycerol, trimethylolethane,trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol,dipentaerythritol, tripentaerythritol, polypentaerythritol, sorbitol,methyl glucosides, sucrose and the like with alkylene oxides such asethylene oxide, propylene oxide, their mixtures, and the like.

A particular class of aromatic polyisocyanates which may be employed inthe novel solvent based coating compositions of the invention arepolymethylene polyphenol isocyanates having the formula: ##STR5##wherein n equals 1 to 3. Such compounds, sold under the tradename "PAPI"by the Upjohn Chemical Company of Kalamazoo, Mich., have proven to beparticularly useful in compositions of the invention, resulting incompositions exhibiting desirable toughness in the final cured coating.

The active hydrogen containing blocking agents which are reacted withthe above described organic diisocyanates may be selected from numerousblocking agents which will be apparent to those skilled in this art.Representative of those blocking agents which are preferred are thoseselected from the group consisting of (i) aliphatic, cycloaliphatic andaromatic alkyl monoalcohols; (ii) hydroxyl amines; (iii) oximes; (iv)lactams; and (v) triazoles. Any suitable aliphatic, cycloaliphatic oraromatic alkyl monoalcohol may be used as a blocking agent in accordancewith the present invention. For example, aliphatic alcohols, such asmethyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, hetpyl, octyl,nonyl, 3,3,5-trimethylhexyl, decyl, and lauryl alcohols, and the likemay be employed. Suitable cycloaliphatic alcohols include, for example,cyclopentanol, cyclohexanol and the like, while aromatic-alkyl alcoholsinclude phenylcarbinol, methylphenylcarbinol, and the like. Minoramounts of even higher molecular weight relatively non-volatilemonoalcohols may be used, if desired, to serve as plasticizers in thecoatings provided by the invention. Examples of hydroxyl amines whichmay be employed as blocking agents include ethanol amine and propanolamine. Suitable oxime blocking agents include, for example,methylethylketone oxime, acetone oxime and cyclohexanone oxime. Examplesof lactams which may be used as blocking agents are epsilon-caprolactam,epsilon-butyrolactam and pyrrolidone, while suitable triazoles includecompounds such as 1,2,4-triazole, 1,2,3-benzotriazole, 1,2,3-tolyltriazole and 4,5-diphenyl-1,2,3-triazole. Particularly preferred activehydrogen containing blocking agents are methylethyl ketoxime and2-ethylhexanol.

(i) Isocyanurate Ring Containing Blocked Isocyanate Compounds

Within the scope of the above general class of blocked polyisocyanatecrosslinking agents, a particular class type of blocked polyisocyanatecrosslinking agent which may be employed in the novel solvent basedcoating compositions of the invention comprises isoycanurate ringcontaining blocked isocyanate compounds. In general, these blockedpolyisocyanates may be formed by blocking with the aforementionedblocking agent isocyanurate ring containing polyisocyanates. Thesecompounds may be formed by cyclotrimerization of difunctionalisocyanates. Usually, the reaction does not stop in this stage andcontinues through the formation of polyfunctional oligomers or a mixtureof such oligomers with a portion of the pure trifunctionalpolyisocyanate. Mixtures of trifunctional product and variouspolyfunctional oligomers are commercially available.

A particular desirable blocked polyisocyanate crosslinking agent is theblocked form of the pure trifunctional isocyanurate represented by thefollowing formula: ##STR6## wherein R is selected from the groupconsisting of aliphatic, cycloaliphatic and aromatic groups andcombinations thereof and B is the residue of an active hydrogencontaining blocking agent. More specifically, this compound is disclosedin U.S. Pat. No. 4,491,663 the disclosure of which is incorporatedherein by reference.

(ii) Oligoester Modified Blocked Polyisocyanates

Still further particular blocked polyisocyanates useful as crosslinkingagents in the novel solvent based coating compositions of this inventionare oligoester modified blocked polyisocyanates prepared from aparticular class of oligoester diols and triols. A first type of sucholigoester modified blocked polyisocyanates is prepared from organicdiisocyanates bearing one isocyanate group more reactive than the other,with the more reactive isocyanate first being blocked with a blockingagent and the remaining isocyanate group then being reacted withhydroxyl functionality of an oligoester diol or triol as referred toabove. The second type of oligoester modified blocked polyisocyanate maybe prepared by reacting oligoester diols from the aforementioned classof oligoesters with an excess of organic diisocyanate so as to form anisocyanate terminated prepolymer followed by blocking of the terminalisocyanate groups of the prepolymer with an active hydrogen containingblocking agent. Each of these materials is particularly useful in thecompositions of the invention and produces final cured coatingcompositions exhibiting outstanding flexibility.

Oligoesters of the type employed in the preparation of thesecrosslinking agents are described in U.S. Pat. No. 4,322,508 issued Mar.30, 1982, the disclosure of which is hereby incorporated by reference.The hydroxy functional oligoesters within the useful class of materials(i) have a number average molecular weight (Mn) of between about 150 andabout 3000, preferably between about 230 and about 1000, (ii) bear 2 or3 hydroxyl groups per molecule, and (iii) are formed by anesterification reaction between a carboxylic acid and an epoxide. Theesterification reaction products are selected from the group consistingof:

(a) the esterification reaction product of polycarboxylic acid, i.e.,carboxylic acid bearing 2 or more carboxyl groups, and monoepoxide;

(b) the esterification reaction product of polyepoxide, i.e., a compoundhaving 2 or more epoxide groups, and monocarboxylic acid, preferablycontaining no ethylenic unsaturation, and bearing no hydroxyfunctionality;

(c) the esterification reaction product of hydroxy functional carboxylicacid and mono- or polyepoxide, preferably monoepoxide;

(d) the esterification reaction product of monocarboxylic acid andhydroxy functional mono- or polyepoxide, preferably monoepoxide; and

(e) mixtures of (a)-(d).

As noted above, the first type of oligoester modified blockedpolyisocyanate crosslinking agent is prepared by (i) reacting organicdiisocyanate bearing one isocyanate group which is more reactive thanthe other with a sufficient amount of an active hydrogen containingblocking agent to react substantially with all of the more reactiveioscyanate groups, thus providing a half-blocked diisocyanate and (ii)reacting this half-blocked intermediate with the above discussedoligoester. The organic diisocyanates employed in this synthesis, aswell as the active hydrogen containing blocking agents, are discussedabove in connection with the preparation of the isocyanurate ringcontaining blocked isocyanate crosslinking agents useful in compositionsof the invention. The organic polyisocyanate-blocking agent adductintermediate is formed by reacting a sufficient quantity of the blockingagent with the organic diisocyanate to insure that one of the two --NCOgroups on the diisocyanate is reacted. The reaction between the organicdiisocyanate and the blocking agent is exothermic; therefore, thediissocyanate and the blocking agent are preferably admixed attemperatures no higher than about 80° C., preferably below about 50° C.,to minimize the exothermic effect.

This intermediate is next reacted with the oligoester diol or trioldescribed above so as to react substantially all free or unblockedisocyanate groups of the diisocyanate/blocking agent intermediate withhydroxyl groups of the oligoester. This reaction is carried outdesirably at a temperature of about 80°-120° C.

As also discussed above, the second type of oligoester modified blockedpolyisocyanate crosslinking agent useful in the novel solvent basedcoating compositions of the invention is prepared by reacting an excessof organic diisocyanate with an oligoester diol from the above describedclass of oligoesters followed by reaction of the terminal isocyanategroups formed on the resultant prepolymer with an active hydrogencontaining blocking agent as described above so as to react withsubstantially all the isocyanate groups. The diisocyanate startingmaterial is used in excess in amounts sufficient to insure that theintermediate is isocyanate terminated. Therefore, it is preferable thatthe organic diisocyanates and the dihydroxy functional oligoester bereacted in a molar ratio of from greater than 1:1 up to 2:1. Numerousdiisocyanates of the type described hereinbefore may be employed in thepreparation of this intermediate. While it is not necessary that oneisocyanate group be more reactive than the other, the preparation ofthis type of crosslinking agent does not preclude the use of suchmaterial.

D. GENERAL DISCUSSION--OTHER ASPECTS OF INVENTION AND OTHER COMPONENTS

The coating compositions of the invention have been found to provide acured coating having the advantageous physical properties describedabove, over a wide range of cure temperatures and a wide range of solidslevels. More specifically, the coating compositions according topreferred embodiments of the invention have been found to cure attemperatures from as low as about 120° C. or less within about 15minutes or less, and yet to cure and suffer no significant loss ofadvantageous physical properties at temperatures as high as about 200°C. or more for periods up to about 60 minutes or more. Consideredtogether with the storage stability of the coating composition, it canbe readily recognized that the present invention provides a highlysignificant advance in the coating composition art.

It will be within the skill of the art to determine the proper volatileorganic content for a given coating composition of the invention and fora given application. Preferred solvents have relatively low volatilityat temperatures appreciably below their boiling points such that solventevaporation is low during storage and/or application of the coatingcomposition to the substrate. A suitable solvent system may include, forexample, toluene, methyl ethyl ketone, isobutyl acetate, xylene,cellosolve acetate, acetone and a mixture of any of them. Other solventswhich may be employed include terpenes, aliphatic and aromatic naphthas,and the like. Additional suitable solvents are commercially availableand will be apparent to the skilled of the art in view of the presentdisclosure.

Any solvent allowed to remain in the cured coating should be inert so asto avoid adverse effect upon the cured coating or upon another coatinglayer used in conjunction with it during the curing process orthereafter. Preferrably, the cured coating is substantially free ofsolvent.

Sufficient solvent is used to reduce the viscosity of the coatingcomposition to a level suitable for application to the substrate in thedesired manner.

Obviously, in those cases where the composition is to be applied as achip resistant primer the amount of solvent will be reduced so as togive a solids level of about 65-80%. Such higher solids materials aregenerally applied using hot spray equipment.

Flow control agent(s), for example, polybutyl acrylate; wettingagent(s), for example, silicone; pigments; pigment dispersants;corrosion inhibitors, for example, chromate pigments, numerous of all ofwhich are known to the skilled of the art, may be employed in thecoating compositions of the invention. In addition, suitable reactiveadditives can be used, including, for example, low molecular weight diolflow control agents and reactive diluents. Compositions of theinvention, and in particular the chip resistant primers of theinvention, may also include anti-settling or anti-sagging agents tocontrol the thixotropic properties of the composition. Exemplary ofavailable materials suitable for this purpose are Dislon (trademark)6900-20X manufactured by Kusumoto Chemicals, Ltd., Tokyo, Japan and soldby King Industries, Norwalk, CT. 06852; Bentone (trademark) 38, N. L.Industries, Highstown, N.J. 08520; and Cab-O-Sil (trademark) M-5, CabotCorporation, Boston, Mass.

Curing the coating composition requires baking for sufficient time atsufficiently elevated temperature to react the crosslinking agent withthe hydroxyl functionality of the hydroxy functional epoxy ester resinand the polycaprolactone diol. The time and temperature required to curethe coating are interrelated and depend upon the particular hydroxyfunctional epoxy ester resin, polycaprolactone diol, crosslinking agent,solvent and other materials, if any, and the amount of each comprisingthe coating composition. The coating compositions according to preferredembodiments of the invention, as described above, have been found toprovide the best coating results when cured at temperature at about 150°C. (300° F.) for 20 minutes. It is a highly significant advantage of theinvention, however, that these same coating compositions can withstand,for example, temperature as high as about 200° C. (390° F.) for periodsof time as long as about 60 minutes. Accordingly, great flexibility isprovided in both designing and implementing a curing schedule for partscoated with the coating compositions of the invention. Thus, in theassembly of automotive vehicles, for example, vehicles unavoidably heldin a curing oven for long periods of time during unplanned assembly lineshut-downs are recovered with cured and unharmed coatings.

High solids coating compositions according to the present invention,comprising the crosslinkable hydroxy functional epoxy resins of theinvention, polycaprolactone diol, especially the preferred resinsdescribed above, polycaprolactone diol, especially the preferredpolycaprolactone diol discussed above and blocked polyisocyanatecrosslinking agent, especially the preferred materials described abovehave been found to afford cured coatings with improved corrosionresistance and chip resistance, thus representing a highly advantageousadvance in the art.

A most preferred use of the coating composition of the invention is as ahigh solids hot sprayable chip resistant primer for use on a bare metalsubstrate such as an automotive vehicle body which is subject tochipping. Primer compositions typically are pigmented and any pigmentscommonly included in primer compositions for metal substrates andacrylic dispersion topcoats such as, for example, carbon black, ironoxide, lithopone, magnesium, silicate, silica, barium sulfate, TiO2,chrome yellow, calcium chromate, strontium chromate, zinc potassiumchromate any the like may be used. The primer can be pigmented accordingto known methods including, for example, by grinding pigments in aportion of the curable resin and adding to the primer composition.

The pigment-to-binder ratio of the chip resistant primer may be fromabout 0.5:1 to about 2:1 by weight, respectively; it is preferred,however, to use a primer having a pigment-to-binder ratio of from about1:1 to about 1.5:1 by weight, respectively.

In preferred embodiments of this invention pigments and thixotropicagents desireably are dispersed with epoxy ester resins. One type ofepoxy ester resin useful for this purpose comprises the reaction productof diepoxide, diphenol and/or dimer acid and a mixture of Soya fattyacid and propionic acid (See Example 4). Other epoxy ester resins usefulfor this purpose are those disclosed in U.S. patent application Ser.Nos. 448,886 filed June 14, 1982 (abandoned), 431,465 filed Sept. 30,1982 (abandoned) and in U.S. Pat. No. 4,491,641, all assigned to theassignee of this application. These resins comprise the simultaneousreaction product of diepoxide with (i) diphenol, dicarboxylic acid or amixture of them in chain extension reaction and (ii) fatty acid in chainterminating esterification reaction. Still other suitable epoxy resinsuseful for dispersing pigment and thixotropic agents will be apparent tothe skilled of the art in view of the present disclosure.

No special expedients are necessary in formulating the primercompositions of this invention. For example, they may be prepared simplyby incorporating the resinous components in a suitable solvent system.Thus, for example, by suitable mixing or agitation, each resinouscomponent may be dissolved in a solvent and the resulting solutionscombined to form finished primer compositions.

The solvent system may be any suitable combination of organic solventsas described above. For a high solids, hot sprayable, automotive vehiclechip resistant primer, the solvent will comprise preferably about 20 toabout 40 percent by weight of the total coating compositions, althoughof course, larger or smaller amounts may be utilized depending upon thesolids content desired.

The primer is generally maintained at about 65 to about 80 percentsolids content for hot spraying purposes with conventional thinners suchas aromatic hydrocarbons, commercial petroleum cuts which areessentially aromatic, and the like, and sprayed onto the metal base orother substrate and cured. The primer may be applied in greaterthickness of 1 to 25 mils wet, preferably 10 to 25 mils wet, in order toobtain final coatings in the desired range of 5-11 mils in regionshighly susceptible to chipping and is then feathered down in thicknessto the thickness of paints in areas not receiving a chip resistantprimer. The primer is cured at elevated temperatures by any convenientmeans such as baking ovens or banks of infra-red heat lamps. Curingtemperatures are preferably from about 135° C. to about 165° C.,although curing temperatures from about 100° C. to about 230° C. may beemployed, if desired.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that the specific examplesare presented by way of illustration and not by way of limitation.Unless otherwise specified, all references to "parts" are intended tomean parts by weight.

EXAMPLE 1 Preparation of Hydroxy Functional Epoxy Ester Resin

In a suitable reactor were charged 353 parts Araldite RD-2, (trademark,Ciba-Geigy Corp., diepoxide), 124 parts azelaic acid and 0.5 partssodium carbonate. The temperature of the mixture was brought to about180° C., at which point an exothermic reaction took place that raisedthe temperature to about 200° C. After one hour, the acid number wasfound to be less than 1. 176 parts of 2,2-bis(hydroxymethyl)propionicacid were added and the temperature was kept at 180° C. for oneadditional hour. The reaction product was then cooled down to 120° C.and 534 parts of M-pyrol were added. The resin had a viscosity of S+ andan acid number less than 0.5 at 55.3% solids (i.e., non-volatilesolids).

EXAMPLE 2 Preparation of Hydroxy Functional Epoxy Ester Resin

In a suitable reactor were charged 519 parts Epon 829 (trademark, ShellChemical Co., diepoxide), and 512 parts Empol 1016 (trademark, EmeryInd., Inc., dimer acid). The temperature of the mixture was brought upto about 180° C. at which point an exothermic reaction took place thatraised the temperature to about 200° C. After one hour, the acid numberwas found to be less then 1. 117 parts of2,2-bis(hydroxymethyl)propionic acid and 0.5 parts of sodium carbonatewere added and the temperature was kept at 180° C. for one additionalhour. The reaction product was then cooled down to 120° C. and 1148parts of M-pyrol were added. The resin had a viscosity of Z₃ + and anacid number less than 1 at 48.2% solids. EXAMPLE 3

Preparation of Hydroxy Functional Epoxy Ester Resin

In a suitable reactor were charged 519 parts Epon 829 (trademark, ShellChemical Co., diepoxide) and 166 parts of azelaic acid. The temperatureof the mixture was brought up to about 180° C. at which point anexothermic reaction took place that raised the temperature to about 200°C. After one hour the acid number was found to be less than 1. 117 partsof 2,2-bis(hydroxymethyl)propionic acid, and 0.5 parts sodium carbonatewere added and the temperature was kept at 180° C. for an additionalhour. The reaction product was then cooled down to 120° and 802 parts ofM-pyrol were added. The resin had a viscosity of Z₃ and an acid number 5at 51.36% solids.

EXAMPLE 4 Preparation of Epoxy-Ester Dispersing Resin

Into a suitable reactor were charged 1280 parts Epon 829 (trademark,Shell Chemical Co., diepoxide), 954 parts Empol 1016 (trademark, EmeryInd., Inc., dimer acid), 364 parts Soya fatty acid, 268 parts2,2-bis(hydroxymethyl)propionic acid and 13 parts of lithiumneodeconoate. The temperature of the mixture was brought up to about180° C., at which point an exothermic reaction took place that raisedthe temperature to about 200° C. After one hour, the acid number wasfound to be less than 2. 940 parts Solvesso 100 and 305 parts Solvesso150 were added, and the mixture was cooled. The resin had a viscosity ofZ₇ at 70.0% solids.

EXAMPLE 5 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor were charged 870 parts methylethyl ketoxime and180 parts Solvesso 100. 1330 parts of PAPI 27 (trademark, The UpJohnCo., aromatic polyisocyanate) was added dropwise to the mixture over twohours; the reaction temperature rose from room temperature to 80°-95° C.39 parts 2-ethylhexanol was added to the mixture and the temperature ofthe mixture was maintained at 85°-95° C. for one hour. At that point,816 parts of M-pyrol was added and the mixture was cooled. The resultingresin was dark brown and had a viscosity of 6000 cps at 67.0% solids.

EXAMPLE 6 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor were charged 537 parts methylethyl ketoxime. 784parts PAPI 94 (trademark, The UpJohn Co., aromatic polyisocyanate) wasadded dropwise over two hours; the reaction temperature rose from roomtemperature to 80°-95° C. The mixture was maintained at 85°-95° C. forone hours. The mixture then was checked to insure complete reaction ofthe isocyanate by infrared spectroscopy. At that point, 300 partsmethylamyl ketone and 150 parts M-pyrol were added and the mixture wascooled. The resulting resin was dark brown and was 75% solids.

EXAMPLES 7-10 Preparation of Blocked Polyisocyanate Crosslinking Agent

Blocked polyisocyanate crosslinkers according to the invention wereprepared in the manner of Example 6. The components employed are shownin the table below.

    ______________________________________                                                      Example                                                                       7    8        9      10                                         Composition     Parts                                                         ______________________________________                                        L-2991 A*       360    360      360                                           Desmodur IL*                         525                                      methyl amyl ketoxime                                                                          174                   87                                      benzotriazole          238                                                    epsilon-caprolactam             228                                           N--methyl pyrolidone                                                                          133    150      195  461                                      % solids         80    80.1     75.1  57                                      Viscosity       Z.sub.1                                                                              Z.sub.6  Z.sub.2                                                                            Z                                        ______________________________________                                         *Trademarks of Mobay Chemical Co.; L2291 A is a biurette of hexamethylene     diisocyanate; Desmodur IL is a polyisocyanurate of tolylene diisocyanate.

EXAMPLE 11 Millbase Preparation

In a one gallon can or ballmill were charged the following materials andone quart of diagonal shot. The mixture was placed on a roller mill for16-24 hours to reach a 7+ hegman dispersion. At that point, the letdownwas added, and the mixture was run an additional hour on the rollermill.

    ______________________________________                                                           Parts                                                      ______________________________________                                                   Hi-Sol #3*    585                                                             2-Ethyl Hexanol                                                                              95                                                             Polyethylene Wax                                                                             70                                                             Anti-Terra-U**                                                                               40                                                             Resin of Example 4                                                                          103                                                             Barytes       2259                                                            TiO.sub.2     429                                                             Carbon Black   29                                                             Strontium Chromate                                                                          143                                                  Letdown:   Resin of Example 4                                                                          247                                                  ______________________________________                                         *Trademark of Ashland Chemical Co., Columbus, Ohio; HiSol #3 is an            aromatic solvent.                                                             **Trademark of Byk Mallinckrodt, Wallingford, CT 06492; AntiTerra-U is an     antisettling and wetting agent.                                          

EXAMPLE 12 Bentone Gel Preparation

To a clean Ball Mill were charged the following:

    ______________________________________                                                               Parts                                                  ______________________________________                                        Solvesso 150             513                                                  Propylene Carbonate      13                                                   Bentone 38               30                                                   Grind 30 minutes, then add:                                                   Resin of Example 4       384                                                  Grind approximately 2 Hrs. to 8 Hegman                                        Letdown with:                                                                 Solvesso 150             60                                                                            1000                                                 ______________________________________                                    

EXAMPLES 13-15

Coating Compositions of the invention were formulated as shown below.

    ______________________________________                                                        Example                                                                       13      14     15                                             Composition       Parts                                                       ______________________________________                                        Resin of Example 1                                                                              1627                                                        Resin of Example 2          1867                                              Resin of Example 3                 1752                                       Millbase of Example 11                                                                          5788      5788   5788                                       TONE 0260.sup.1 (trademark)                                                                     950        950   950                                        Bentone Gel of Example 12                                                                       2315      2315   2315                                       Crosslinker of Example 5                                                                        984              984                                        Crosslinker of Example 6    1050                                              Dislon.sup.2      114        120   114                                        Cab-O-Si1.sup.3   142              142                                        ______________________________________                                         .sup.1 Trademark of Union Carbide, Danbury, Conn., TONE 0260 is a             polycaprolactone diol.                                                        .sup.2 Trademark of Kusumoto Chemicals, Ltd., Dislon is an antisagging        agent.                                                                        .sup.3 Trademark of Cabot Corp., Boston, Mass.; CabO-Sil is a fumed silic     (antisettling agent).                                                    

The coating compositions were prepared by sequential mixing in a 5gallon working capacity EMCO Proto-Lab SW Mill (trademark), Epworth Mfg.Co., South Haven, Mich., set at 900 rpm. Resin and Dislon (trademark)were first mixed for approximately 10 minutes and then millbase, Bentonegel and crosslinker were added sequentially while mixing. Finally,Cab-O-Sil (trademark) was added and the composition mixed until a grindof 6+ on the Hegman scale was obtained.

The above compositions were sprayed at 140°-160° C. using hot-sprayequipment commercially available from Nordson Corp. Unpolished Bonderitesteel panels were sprayed and baked at 135° C. for 20 minutes. Thethickness of the coating tested varied from 5 mils to 12 mils. Thepanels were top-coated with white enamel and tested for chip resistanceusing 10 pts. of gravel in the gravelometer test. All the abovecompositions exhibited excellent chip resistance. In addition, panelswere tested for corrosion resistance (500 hrs. salt spray test, scribedpanels) and humidity resistance with excellent results.

EXAMPLES 16-19

Additional coating compositions according to the invention are shownbelow.

    ______________________________________                                                       Example                                                                       16     17     18       19                                      Composition      Parts                                                        ______________________________________                                        Resin of Example 2                                                                             1867     1867   1867   1867                                  TONE 0260.sup.1   950      950    950    950                                  Millbase of Example 11                                                                         5788     5788   5788   5788                                  Gel of Example 12                                                                              2315     2315   2315   2315                                  Crosslinker of Example 7                                                                        922                                                         Crosslinker of Example 8   922                                                Crosslinker of Example 9          984                                         Crosslinker of Example 10               1294                                  Dislon.sup.2      100      100    100    100                                  ______________________________________                                         .sup.1 Trademark of Union Carbide, Danbury, Conn. TONE 0260 is a              polycaprolactone diol.                                                        .sup.2 Trademark of Kusumoto Chemicals, Ltd. Dislon is an antisagging         agent.                                                                   

INDUSTRIAL APPLICATION

It will be apparent from the foregoing that this invention hasindustrial applicability as a coating composition, especially as a hotsprayable, high solids coating composition suitable for use as a chipresistant automotive vehicle primer adapted for use on body panel areassubject to chipping by stones, gravel and other road debris.

In view of this disclosure, many modifications of this invention will beapparent to those skilled in the art. It is intended that all suchapparent modifications fall within the true scope of this invention andbe included within the terms of the appended claims.

What is claimed is:
 1. A organic solvent based, thermosetting coatingcomposition comprising:(A) hydroxy functional epoxy ester resin having anumber average molecular weight (M_(n)) between about 1,000 and about4,000, and being the reaction product of diepoxide with dicarboxylicacid in chain extension and acid component in chain termination inapproximately a 1 to 1 equivalent ratio with the chain extended reactionproduct, said acid component comprising primary hydroxy functional acid;(B) linear polycaprolactone diol having a molecular weight between about1500 and about 5000, wherein said (A) and (B) are included in saidcomposition in a weight ratio between about 4:1 and 1:4; and (C) blockedpolyisocyanate crosslinking agent comprising at least two isocyanategroups which have been blocked by reaction with an active hydrogenbearing blocking agent, which crosslinking agent de-blocks at the curetemperature of said composition, said crosslinking agent being includedin said composition in an amount equal to between about 10 and about 50percent of the combined weight of said (A) and (B) in said composition.2. A solvent based, thermosetting coating composition in accordance withclaim 1, wherein said hydroxy functional epoxy ester resin is thereaction product of said diepoxide with said dicarboxylic acid and,subsequently, with said acid component.
 3. A solvent based,thermosetting coating composition in accordance with claim 1, whereinsaid hydroxy functional epoxy ester resin is the reaction product ofsaid diepoxide with said dicarboxylic acid and substantiallysimultaneously with said acid component.
 4. A solvent based,thermosetting coating composition in accordance with claim 1, whereinsaid polycaprolactone diol has a molecular weight between about 2,000and 4,000.
 5. A solvent based, thermosetting coating composition inaccordance with claim 1, wherein said (A) and (B) are included in saidcomposition in a weight ratio of about 1:1.
 6. A solvent based,thermosetting coating composition in accordance with claim 1, whereinsaid blocked polyisocyanate crosslinking agent is included in saidcomposition in an amount between about 20 and about 40 percent of thecombined weight of components (A) and (B) in said composition.
 7. Asolvent based, thermosetting coating composition in accordance withclaim 1, wherein said diepoxide is selected from the group consisting ofbisphenol-A epichlorohydrin epoxy resin, hydantoin epoxy resin, cyclicand acyclic aliphatic diepoxides and mixtures thereof.
 8. A solventbased, thermosetting coating composition in accordance with claim 1,wherein said dicarboxylic acid is selected from the group consisting ofsubstantially saturated acyclic aliphatic dimer acids of about 4-42carbons.
 9. A solvent based thermosetting coating composition inaccordance with claim 1, wherein said primary hydroxy functional acid isselected from C₃ -C₂₆ acids bearing a single carboxyl group, at leastone primary hydroxyl group, and no additional functionality which wouldreact substantially with the chain extension reactants or reactionproduct.
 10. A solvent based, thermosetting coating composition inaccordance with claim 1, wherein said primary hydroxy functional acid isselected from the group consisting of dimethylolpropionic acid,bis(hydroxyethyl)propionic acid, bis(hydroxypropyl)propionic acid andmixtures thereof.
 11. A solvent based, thermosetting coating compositionin accordance with claim 1, wherein said acid component furthercomprises fatty acid.
 12. A solvent based, thermosetting coatingcomposition in accordance with claim 11, wherein said fatty acid isselected from the group consisting of Soya fatty acid, butyric, lauric,palmitic and stearic fatty acids and mixtures thereof.
 13. A solventbased, thermosetting coating composition in accordance with claim 1,wherein said polycaprolactone diol is the product of polymerization oflactone monomers in the presence of initiator compounds having twofunctional groups each having an active hydrogen capable of opening thelactone ring at a temperature between about 50° C. and about 300° C.,said lactone monomers having the general formula: ##STR7## wherein n isat least 4, at least n+2 R's are H and the remaining R's aresubstituents selected from the group consisting of alkyl, cycloalkyl,alkoxy and single ring aromatic hydrocarbon radicals.
 14. A solventbased, thermosetting coating composition in accordance with claim 13,wherein said lactone monomers comprise unsubstitutedepsilon-caprolactone monomers.
 15. A solvent based, thermosettingcoating composition in accordance with claim 13, wherein said initiatorcompounds are selected from diamines, diols, amino alcohols, diacids andhydroxy-carboxylic acids.
 16. A solvent based, thermosetting coatingcomposition in accordance with claim 1, wherein said blockedpolyisocyanate crosslinking agent comprises blocked polymethylenepolyphenol isocyanate which unblocked has the formula: ##STR8## whereinn equals 1 to
 3. 17. A solvent based, thermosetting coating compositionin accordance with claim 1, wherein polyisocyanate employed in thepreparation of said blocked polyisocyanate crosslinking agent comprisesisocyanurate ring containing polyisocyanate prepared bycyclotrimerization of diisocyanate.
 18. A solvent based, thermosettingcoating composition in accodance with claim 1, wherein said blockedpolyisocyanate crosslinking agent is the reaction product of:(a) thereaction product of (i) organic diisocyanate represented by the formula:

    OCN--R--NCO

wherein R is selected from the group consisting of aliphatic,cycloaliphatic and aromatic radicals and combinations thereof andwherein one of the isocyanate groups thereof is a more reactiveisocyanate group than the other and (ii) sufficient active hydrogencontaining blocking agent to react with substantially all of said morereactive isocyanate groups; and (b) sufficient polyol to react withsubstantially all of said other isocyanate groups.
 19. A solvent based,thermosetting coating composition in accordance with claim 1, suitableto be used as a chip resistant primer to be sprayed at elevatedtemperature, wherein the solids level of the composition is in the rangeof 60-80% by weight.
 20. An organic solvent based, thermosetting coatingcomposition comprising: A. hydroxy functional epoxy ester resin having anumber average molecular weight (M_(n)) of between about 1,000 and about4,000, and being the reaction product of (i) diepoxide selected from thegroup consisting of bisphenol-A epichlorohydrin epoxy resin, hydantoinepoxy resin, cyclic and acyclic aliphatic diepoxide and mixturesthereof, (ii) dicarboxylic acid consisting essentially of thedimerization product of C-18 fatty acid, and (iii) acid componentcomprising primary hydroxy functional primary acid selected from thegroup consisting of dimethylolpropionic acid, bis(hydroxyethyl)propionicacid, bis(hydroxypropyl)propionic acid and mixtures thereof said hydroxyfunctional epoxy ester resin being the reaction product of saiddiepoxide and said dicarboxylic in chain extension and thereafter inchain termination with said acid component in approximately a 1 to 1equivalent ratio;(B) linear polycaprolactone diol having a molecularweight between about 1500 and about 5000 made by polymerizingepsilon-caprolactone monomers in the presence of initiator compoundshaving two functional groups each having an active hydrogen capable ofopening the lactone ring at a temperature between about 130° C. andabout 200° C., wherein said (A) and (B) are included in said compositionin a weight ratio between about 4:1 and 1:4; and (C) blockedpolyisocyanate crosslinking agent comprising at least two isocyanategroups which have been blocked by reaction with an active hydrogenbearing blocking agent which un-blocks at the cure temperature of saidcomposition, said blocked polyisocyanate being selected from blockedaliphatic, aromatic, cycloalkylene, aliphatic aromatic, and nuclearsubstituted aromatic polyisocyanates and being included in saidcomposition in an amount equal to between about 10 and 50 percent of thecombined weight of said (A) and (B) in said composition.